Method for isolating a fault and restoring power in an underground radial loop network using fault interrupting switches

ABSTRACT

A method for isolating a fault in an underground power distribution network. The network includes a power line, a plurality of transformers electrically coupled to and positioned along the power line, a first end switch connected to one end of the power line and a second end switch connected to an opposite end of the power line, where each transformer includes an upstream switching device and a downstream switching device, and where source power is provided to both ends of the power line through the first and second end switches and one of the switching devices is a normally open switching device. The method includes detecting overcurrent in the network from the fault, opening certain ones of the switching devices in response thereto, detecting loss of voltage as a result of the open switching devices and opening or closing certain ones of the switching devices to isolate the fault.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from the U.S.Provisional Application No. 63/085,441, filed on Sep. 30, 2020, thedisclosure of which is hereby expressly incorporated herein by referencefor all purposes.

BACKGROUND Field

The present disclosure relates generally to a switching device thatprovides fault isolation and restoration in a power distribution networkand, more particularly, to a switching device that is part of atransformer in an underground residential power distribution network andthat provides fault isolation and restoration.

Discussion of the Related Art

An electrical power distribution network, often referred to as anelectrical grid, typically includes a number of power generation plantseach having a number of power generators, such as gas turbines, nuclearreactors, coal-fired generators, hydro-electric dams, etc. The powerplants provide power at a variety of medium voltages that are thenstepped up by transformers to a high voltage AC signal to be connectedto high voltage transmission lines that deliver electrical power to anumber of substations typically located within a community, where thevoltage is stepped down to a medium voltage for distribution. Thesubstations provide the medium voltage power to a number of three-phasefeeders including three single-phase feeder lines that carry the samecurrent, but are 120° apart in phase. A number of three-phase and singlephase lateral lines are tapped off of the feeder that provide the mediumvoltage to various distribution transformers, where the voltage isstepped down to a low voltage and is provided to a number of loads, suchas homes, businesses, etc.

Periodically, faults occur in the distribution network as a result ofvarious things, such as animals touching the lines, lightning strikes,tree branches falling on the lines, vehicle collisions with utilitypoles, etc. Faults may create a short-circuit that increases the load onthe network, which may cause the current flow from the substation tosignificantly increase, for example, many times above the normalcurrent, along the fault path. This amount of current causes theelectrical lines to significantly heat up and possibly melt, and alsocould cause mechanical damage to various components in the substationand in the network. Power distribution networks of the type referred toabove often include a number of switching devices, breakers, reclosers,interrupters, etc. that control the flow of power throughout thenetwork, and may be used to isolate faults within a faulted section ofthe network.

As part of their power distribution network, many utility companiesemploy a number of underground single-phase lateral circuits that feedresidential and commercial customers. Often times these circuits areconfigured in a loop and fed from both ends, where an open location,typically at a transformer, is used in the circuit to isolate the twopower sources. Although providing underground power cables protectscircuits from faults created by things like storms and vegetationgrowth, underground cables still may break or otherwise fail as a resultof corrosion and other things. For a residential loop circuit of thetype referred to above having two power sources, it is usually possibleto reconfigure the open location in the circuit so that loads that areaffected by a fault are fed by the other source and service to all ofthe loads is maintained. However, known processes for identifying thelocation of a cable failure and the subsequent reconfiguration of theopen location often results in long power restoration times.

SUMMARY

The following discussion discloses and describes a method for isolatinga fault in an underground power distribution network. The networkincludes a power line, a plurality of transformers electrically coupledto and positioned along the power line, a first end interrupter switchconnected to one end of the power line and a second end interrupterswitch connected to an opposite end of the power line, where eachtransformer includes an upstream switching device and a downstreamswitching device, and where source power is provided to both ends of thepower line through the first and second end interrupter switches and oneof the switching devices is a normally open switching device. The methodincludes detecting overcurrent in the network from the fault and thenopening one or more of the one end switch that is delivering power to asection of the network that has the fault and at least one of theswitching devices in the section between the one end switch and thefault. The method also includes detecting loss of voltage by theswitching devices that are between the fault and the normally openswitching device, and closing the switching devices that detect voltageon their upstream side and do not detect the overcurrent when theyclose. The method further includes closing the normally open switchingdevice if it detects voltage on its upstream side and does not detectthe overcurrent when it closes, and closing and then opening thoseswitching devices that detect voltage on their upstream side and detectthe overcurrent.

Additional features of the disclosure will become apparent from thefollowing description and appended claims, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of a known power distributionnetwork including an underground residential power circuit;

FIG. 2 is an isometric view of a known transformer used in the circuitshown in FIG. 1;

FIG. 3 is a simplified schematic diagram of the power distributionnetwork shown in FIG. 1 where the transformers include a pair of faultinterrupting switching devices;

FIG. 4 is an isometric view of the transformer shown in FIG. 2 andincluding the fault interrupting switching devices;

FIG. 5 is an isometric view of one of the fault interrupting switchingdevices separated from the transformer;

FIG. 6 is a cross-sectional type view of the fault interruptingswitching device shown in FIG. 5;

FIG. 7 is an isometric view of a sectionalizer switching device that canbe employed in the transformer instead of the fault interruptingswitching devices;

FIG. 8 is a cross-sectional type view of the sectionalizer switchingdevice shown in FIG. 7;

FIG. 9 is a side view of the sectionalizer switching device shown inFIG. 7 illustrating conductors in the device;

FIG. 10 is an isometric view of the transformer shown in FIG. 2including two of the sectionalizer switching devices shown in FIGS. 7-9;

FIG. 11 is a schematic block diagram of a switch assembly including twoof the sectionalizer switching devices sharing a common control board;

FIG. 12 is a schematic block diagram of the control board in the switchassembly;

FIG. 13 is an isometric view of the transformer shown in FIG. 10 andincluding parking stands; and

FIG. 14 is a simplified schematic diagram of a residential powerdistribution network of the type including transformers having a pair ofswitching devices that are either fault interrupting devices orsectionalizer devices, where the network is used to describe faultisolation and power restoration for situations where a fault occurs inthe network or there is a loss of voltage upstream of the network.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the disclosure directedto a switching device that provides fault isolation and restoration ismerely exemplary in nature, and is in no way intended to limit theinvention or its applications or uses. For example, the switchingdevices discussed herein have particular application for use withtransformers employed in underground residential circuits. However, theswitching devices may have other applications.

This disclosure proposes hardware and algorithms for the automaticprotection, isolation and restoration of underground residential cableloops and methods to switch cable segments without handling cableelbows. The system and method provide automation without communicationsto a central controller, automation without having to configure deviceparameters, such as IP addresses, even when the automation requirescommunications between devices, provides coordinated protection throughcommunications-less coordination with a recloser, provides forelimination of load switching and fault making with cable elbows, andcontrols packaging that can be replaced and upgraded in the field as newfeatures become available.

FIG. 1 is a simplified schematic diagram of a known power distributionnetwork 10 including an over-head section 12 having a three-phase feeder14, or possibly a single-phase feeder, and a single-phase undergroundresidential loop section 16 including a single-phase lateral line 18having one end 22 coupled to the feeder 14 through a fuse 24 and anopposite end 28 coupled to the feeder 14 through a fuse 30, where thefuses 24 and 30 may be pole mounted or pad mounted fuses. Although thisembodiment shows the ends 22 and 28 connected to the feeder 14, in analternate embodiment the ends 22 and 28 may be coupled to differentfeeders. Further, the ends 22 and 28 would generally be coupled to thesame phase of the feeder 14. The fuses 24 and 30 can be any suitableswitching device for the purposes described herein that disconnects theline 18 from the feeder 14, such as a fault interrupting device orreclosing device. The medium voltage provided on the line 18 is steppeddown to a low voltage by a number of transformers suitable to providepower to a number of loads 34, such as homes. In this non-limitingembodiment, the circuit 16 includes three transformers 40, 42 and 44each including a primary coil 46 across which the medium voltage isapplied and a secondary coil 48 that provides low voltage to a serviceconductor 50 to which the loads 34 are coupled. However, as will beappreciated by those skilled in the art, a typical underground loopcircuit of this type will include several more transformers.

FIG. 2 is an isometric view of the transformer 40 of the type that ismounted on a pad (not shown) with the understanding that thetransformers 42 and 44 are the same or similar. The transformer 40includes an enclosure 60 that houses the coils 46 and 48 and otherelectrical components (not shown) of the transformer 40. A cover 58 ofthe enclosure 60 is shown in an open position to expose a panel 62 inthe enclosure 60. A connector bushing 64 extends through the panel 62that accepts an elbow connector 66 that connects the line 18 to theprimary coil 46 and a connector bushing 68 extends through the panel 62that accepts an elbow connector 70 that connects the line 18 to theprimary coil 46. A number of positive and negative 120 V lines 72 and 74and a neutral line 76 are connected to the secondary coil 48, extendfrom the housing 60 and provide power along the service conductor 50,where the number of the lines 72 and 74 depends on the number and typeof the loads 34 being serviced by that transformer. A parking stand 78is welded to the panel 62 and is a fixture that allows one of the elbowconnectors 66 and 70 to be supported when it is detached from thebushing 64 or 68 for reasons that will become apparent from thediscussion below.

Power is provided to both ends 22 and 28 of the line 18 and as such oneof the elbow connectors is disconnected from one of the transformers 40,42 or 44 and placed in a bushing (not shown) in the parking stand 78while it is hot to electrical separate the part of the line 18 thatreceives power from the end 22 and the part of the line 18 that receivespower from the end 28. For example, the right side of the transformer 40is disconnected from the line 18 so that the loads 34 connected to thetransformer 40 receive power from the end 22 of the line 18 and theloads 34 connected to the transformers 42 and 44 receive power from theend 28 of the line 18.

Faults occur even for underground lines from, for example, deteriorationof the cable insulation. If a fault 80 occurs, for example, in a section82 of the line 18 between the transformers 42 and 44, the fuse 30 willoperate to clear the fault 80 so that power is prevented from beingprovided to the loads 34 being serviced by the transformers 42 and 44.The utility will be notified of the fault 80 is some manner, such as anautomatic transmission or customer notification, and a procedure is thenimplemented by the utility that requires workers to manually perform aprocess for restoring power to the loads 34 serviced by the transformers42 and 44. For this example, the procedure requires identifying thelocation of the fault 80 by driving a service truck between the fuse 30and the transformers 40, 42 and 44, disconnecting the line 18 from thetransformers 42 and 44 and closing the fuse 30 to see when the fuse 30trips and when it does not. Once the location of the fault 80 isidentified, then the right side of the transformer 42 is disconnectedfrom the line 18 and placed in the parking stand, the left side of thetransformer 44 is disconnected from the line 18 and place in the parkingstand and the line 18 is connected to the right side of transformer 40so that power is provided from the end 22 of the line 18 to the loads 34serviced by the transformers 40 and 44 and power is provided from theend 28 of the line 18 to the loads 34 serviced by the transformer 42.Such a procedure may take hours to restore power to the loads 34serviced by the transformers 42 and 44 even assuming everything goessmoothly.

FIG. 3 is a schematic diagram of the network 10 where each transformer40, 42 and 44 now includes a pair of fault interrupting switchingdevices that provide automatic power restoration to the loads 34 inresponse to a fault, as will be described in detail below. Particularly,the transformer 40 includes a fault interrupting switching device 90coupled between the line 18 and the primary coil 46 and a normally open(NO) fault interrupting switching device 92 coupled between the line 18and the primary coil 46, the transformer 42 includes a faultinterrupting switching device 94 coupled between the line 18 and theprimary coil 46 and a fault interrupting switching device 96 coupledbetween the line 18 and the primary coil 46, and the transformer 44includes a fault interrupting switching device 98 coupled between theline 18 and the primary coil 46 and a fault interrupting switchingdevice 100 coupled between the line 18 and the primary coil 46. Insteadof putting the elbow connector at the right side of the transformer 40in the parking stand 78, the switching device 92 is opened.Additionally, the fuses 24 and 30 have been replaced with single-phase,self-powered, magnetically actuated reclosers 86 and 88.

FIG. 4 is an isometric view of the transformer 40 now shown with theswitching devices 90 and 92 in place. Particularly, the switching device90 is coupled to the bushing 64 and the elbow connector 66 and theswitching device 92 is coupled to the bushing 68 and the elbow connector70.

FIG. 5 is an isometric view and FIG. 6 is a cross-sectional view of theswitching device 90 separated from the transformer 40. The device 90includes an outer grounded enclosure 102 having a special configurationto hold the various components therein. A mounting plate 104 is securedto the enclosure 102 and provides an interface to mount the device 90 tothe panel 62. A transformer interface 106 extends from the enclosure 102and is configured to be electrically coupled to the bushing 64 and aload-break connector interface 108 extends from the enclosure 102 and isconfigured to be electrically coupled to the elbow connector 66. Amanual operating handle 110 allows the device 90 to be manually openedand closed, if necessary.

The enclosure 102 defines an internal chamber 112 in which is configuredthe various components of the device 90. Those components include avacuum interrupter 116 having a vacuum housing 120 defining a vacuumchamber, a fixed upper terminal 122 extending through a top end of thehousing 120 and into the vacuum chamber and a movable lower terminal 126extending through a bottom end of the housing 120 and into the vacuumchamber, where a bellows (not shown) allows the movable terminal 126 toslide without affecting the vacuum in the vacuum chamber. The upperterminal 122 goes into the page and is connected to the transformerinterface 106 and the lower terminal 126 is connected to the load-breakinterface 108 through a flexible connector 134. A high impedanceresistive element 130 is helically wound around the housing 120 and isconnected to the upper terminal 122 at one end to provide a current flowfor energy harvesting purposes when the vacuum interrupter 116 is open.A Rogowski coil 136 or other current sensor, well known to those skilledin the art, is wrapped around the terminal 126 and measures current flowby means of the voltage that is induced in the coil 136 beingproportional to the rate of change of current flow. It is noted that theswitching device 90 including the vacuum interrupter 116 can have otherdesigns consistent with the discussion herein.

The movable terminal 126 is coupled to a rod 138 that is coupled to aplate 140, which in turn is coupled to an actuator assembly 142 havingan electromagnetic actuator 144 and an opening spring 146, where othercompliance springs (not shown) may also be included. The actuatorassembly 142 can be any suitable actuator system for the purposesdescribed herein and may, for example, include an armature that is movedby an opening coil to open the vacuum interrupter 116 and is moved by aclosing coil to close the vacuum interrupter 116, where the armature anda stator provide a magnetic path for the flux produced by the coils. Thecoils are de-energized after the actuator 144 is moved to the open orclosed position, and permanent magnets (not shown) are used to hold thearmature against a latching surface in the open or closed position. Theoperating handle 110 is connected to a rod 150, which is coupled to therod 138. When the handle 110 is rotated in the clockwise orcounter-clockwise direction, the rod 150 moves up or down to manuallyopen or close the vacuum interrupter 116. The vacuum interrupter 116,the Rogowski coil 136 and the actuator assembly 142 are all at mediumvoltage potential, and as such are encapsulated in an insulatingmaterial 152, such as an epoxy, that fills most of the chamber 112.

An electronics control board 160 is provided within the chamber 112 andincludes various electrical components, such as a microprocessor, etc.,where the board 160 is powered through the vacuum interrupter 116 whenit is closed and through the high impedance element 130 when the vacuuminterrupter 116 is open. More particularly, current flows through thelower impedance vacuum interrupter 116 when it is closed and not throughthe element 130, but flows through the element 130 when the vacuuminterrupter 116 is open. Current flow through the element 130 providespower to operate the electronics on the board 160 and operate theactuator assembly 142 to close the vacuum interrupter 116. A highvoltage capacitor 164 and an energy storage capacitor 166 areelectrically coupled to the board 160. One side of the capacitor 164 iscoupled to the board 160 at high voltage and the opposite side of thecapacitor 164 is coupled to the grounded enclosure 100, which provides aconstant impedance and current that allows voltage measurements. Whenthe vacuum interrupter 116 is closed the capacitor 164 provides aconstant current that is used to power the board 160, operate theactuator 144 and charge the storage capacitor 166. When the vacuuminterrupter 116 is open and current is flowing through the element 130if it is available the capacitor 164 also provides a constant currentthat is used to power the board 160, operate the actuator 144 and chargethe storage capacitor 166. The energy stored in the storage capacitor166 can be used when the vacuum interrupter 116 is open or closeddepending on what power is available through the vacuum interrupter 116or the element 130. A dielectric material 168 that takes the shape ofits container and sets, such as epoxy, potting, silicone foam or gel,etc., is provided in the chamber 110 to electrically isolate the highvoltage on the electronics board 160 with the grounded enclosure 100.Because the vacuum interrupter 116, the actuator assembly 112 and thecontrol board 160 all operate at the line voltage and thus have afloating reference potential, the device 90 can be made smaller thanotherwise would be possible since these components do not need to beelectrically isolated.

If the fault 80 occurs in the section 82 of the line 18 between thetransformers 42 and 44, the devices 94 and 96 detect overcurrent andwill open and interrupt the flow of current. The devices 98 and 100 willsee loss of voltage, will not detect overcurrent and will open. A faulthunting algorithm is then performed to isolate the fault and restorepower to the loads 34, as described below. The device 94 will detectvoltage on its source side, but no voltage on its downstream side andwill close after a period of time, and since it does not detect faultcurrent will remain closed. At about the same time, the device 92 willdetect voltage on its primary source side, but no voltage on itsalternate source side and will close, and since it does not detect faultcurrent will remain closed. When the device 94 closes, the device 96will detect voltage on its upstream source side and no voltage on itsdownstream side and will close, but will detect fault current, and willimmediately open within, for example, one current cycle time. At thesame time, when the device 92 closes, the device 100 will detect voltageon its downstream side, but no voltage on its upstream side and willclose, and since it does not detect fault current will remain closed.When the device 100 closes, the device 98 will detect voltage on itsupstream source side and no voltage on its downstream side and willclose, but will detect fault current, and will immediately open. Thus,the fault 80 is isolated between the devices 96 and 98 and power isrestored to all of the loads 34, where the process will take less than aminute.

Fault interrupting switching devices of the type just described can becomplex devices that measure voltage, which requires a referencepotential. A utility may want to employ less expensive or lesssophisticated switching devices, such has sectionalizers, that do notprovide fault interrupting and may not include voltage sensors and canonly measure current. A sectionalizer is generally a self-contained,circuit-opening device used in combination with source-side protectivedevices, such as reclosers or circuit breakers, to automatically isolatefaulted sections of an electrical distribution network. Sectionalizersare typically distributed between and among the reclosers to provide asystem for isolating smaller sections of the network in response to afault. Sectionalizers rely on observing a sequence of fault currentsand/or the presence and absence of voltage either to indicate thepresence of a fault or count the number of reclosing attempts, and thenperform circuit isolation sectionalizing when the maximum number ofreclosing attempts has been reached. Existing power distribution circuitsectionalizers detect the passage of fault currents, including both theinitial fault event and subsequent recloser-initiated events, as part ofmore elaborate fault isolation and restoration processes. Theseprocesses may include counting discrete intervals of fault currentpassage, or counting discrete intervals of voltage presence and absence.In the cases where the particular device is not able to measure voltage,the fault location and isolation schemes discussed above can beaugmented using a revised fault location and isolation scheme proposedbelow.

For the fault interrupting switching devices discussed above, each ofthe devices included its own electronics board that operated at afloating potential relative to the line voltage. In an alternateembodiment, the electronics are removed from the devices and provided asa single electronics unit for both of the devices in each of thetransformers 40, 42 and 44, where the electronics unit operates atground potential. In this embodiment, the devices can operate as faultinterrupting devices or sectionalizers. As used herein, sectionalizersdetect overcurrent, but do not provide reclosing, increase a count eachtime they detect loss of voltage during a fault clearing operation, andlock open if their count has reached a predetermined value and nocurrent is flowing through the device in response to receiving amessage. Capacitors are used for voltage sensing and power linecommunications.

FIG. 7 is an isometric view and FIG. 8 is a cross-sectional view of aswitching device 180 that can be configured to provide both faultinterrupting and sectionalizing, where sectionalizing for thisdiscussion is similar to the traditional sectionalizer with somedifferences. The device 180 includes an outer enclosure 182, atransformer interface 184, a load-break connector interface 186 and amanual handle 188 configured in a similar manner as the device 90 andoperating in a similar manner. The components within the enclosure 182are encapsulated within an insulating medium 190, such as an epoxy,where many of the components are conductors operating at the mediumvoltage potential. FIG. 9 is a side view of the switching device 180with the outer enclosure 182 and the insulating medium 190 removed toshow the conductors.

The switching device 180 includes a vacuum interrupter 196 having avacuum enclosure 198 defining a vacuum chamber 200, an upper fixedterminal 202 extending through the enclosure 198 and into the chamber200 and having a contact 204 and a lower movable terminal 206 extendingthrough the enclosure 198 and into the chamber 200 and having a contact208, where a gap 210 is provided between the contacts 204 and 208 whenthe vacuum interrupter 196 is open. A bellows 212 allows the movableterminal 206 to move without affecting the vacuum integrity of thechamber 200. The movable terminal 206 is coupled to a drive rod 214 thatis coupled to an actuator assembly 216 of the type discussed above foropening and closing the vacuum interrupter 196. In this design, theactuator assembly 216 is insulated and not at the line potential. Asabove, the details of the vacuum interrupter 196 are merely forillustrative purposes in that other designs will be applicable.

A cup-shaped conductor 220 is provided around a top end of the enclosure198 and is electrically coupled to the fixed terminal 202 and to anelbow conductor 222 that is electrically coupled to the connectorinterface 186. An hour glass or cylindrical shaped conductor 224 isprovided around a bottom end of the enclosure 198 and is electricallycoupled to the movable terminal 206. The cup-shaped conductor 220includes an orifice 228 that accepts an end 230 of an elbow conductor232 in an electrically coupled slidable engagement so that the elbowconductor 232 can slide relative to the cup-shaped conductor 220 andstill maintain electrical contact therewith. The conductor 224 includesan orifice 234 that accepts an end 236 of a rod conductor 238 in anelectrically coupled slidable engagement so that the conductor 238 canslide relative to the conductor 224 and still maintain electricalcontact therewith, where the conductor 238 is part of a cylindricaltransformer conductor 240 that is electrically coupled to thetransformer interface 184. The elbow conductor 222 is coupled to thecup-shaped conductor 220 in the same manner. Therefore, when theconductors 220, 222, 224, 232 and 238 are placed in a mold (not shown)and heated insulating material is injected around them, the conductors220, 222, 224, 232 and 238 are able to slide relative to each other asthe insulating material cools and shrinks without affecting theelectrical connections.

The elbow conductor 232 is also electrically coupled to one end of apair of capacitors 242 and 244 and a conductor 246 is electricallycoupled to an opposite end of the capacitors 242 and 244, where the endof the capacitors coupled to the elbow conductor 232 is at linepotential and the end of the capacitors 242 and 244 coupled to theconductor 246 is at or near ground potential, and thus provide stablevoltage coupling for power line communications signals, provide voltagecoupling for voltage sensing, help determine power flow direction andhelp determine the distance to a fault.

FIG. 10 is an isometric view of a transformer 250 that is similar to thetransformer 40 except that the switching devices 90 and 92 have beenreplaced with switching devices 252 and 254 that are identical and arethe same as or similar to the device 180, where like elements areidentified by the same reference number. The conductors in both of thedevices 252 and 254 are connected to a common control unit 256 thatcontrols both of the devices 252 and 254, where the control unit 256 ismounted to the panel 62. In this embodiment, the control unit 256 ispowered by 120 V ac from the lines 72 and 74 through lines 258.

FIG. 11 is a schematic block diagram of a switch assembly 260 includinga switch circuit 262 representing the switching device 252, a switchcircuit 264 representing the switching device 254 and a control board266 representing the control unit 256. The circuit 262 includes a vacuuminterrupter 268, an actuator 270, a Rogowski coil 272 and a capacitor274 and the circuit 264 includes a vacuum interrupter 276, an actuator278, a Rogowski coil 280 and a capacitor 282 operating as discussedabove. The circuit 262 includes a limit switch 284 and the circuit 264includes a limit switch 286 that tell the control board 266 whichposition the device 188 on each of the devices 258 and 252 currentlyholds. Voltage sensing is accomplished by the coupling capacitors 274and 282 that provide a constant current to a resistor (not shown) in thecontrol board 266 and the voltage is measured across the resistor. Thecontrol board 266 is powered by a 120 Vac source 290 from the secondarycoil 48 and a 9V dc battery 292, and may provide signals to acommunications device 294, such as a utility radio.

The control board 266 can be configured with any suitable components andsoftware that perform any desired function consistent with thediscussion herein. FIG. 12 is a schematic diagram of the control board266 showing one non-limiting example. The control board 266 includes amicrocontroller 300 that receives the various inputs, performs thevarious algorithms and provides the various outputs. Signals arereceived from and provided to various elements with respect to themicrocontroller 300. These elements include measured voltages for bothof the switching circuits 262 and 264 at boxes 302 and 304,respectively, high gain at box 306 for the Rogowski coils 274 and 280,low gain at box 308 for the Rogowski coils 274 and 280, ultra-gain atbox 310 for the Rogowski coils 274 and 280, and a modem 312 that providesignals to an analog-to-digital (ADC) converter 314. Further, theelements include handle position at box 316 that links up with the limitswitches 284 and 286, a ferroelectric random access memory (FRAM) 318, arelay 320 and a crystal oscillator 322. The elements further include aninsulated gate bipolar transistor (IGBT) module 326, a half-waverectifier 328 and voltage converters 330, 332, 334, 336 and 338.

By employing the switching devices in connection with the transformersas discussed above, the known parking stand 78 may be obscured and notusable, i.e., blocked by the control unit 256, which may not beacceptable. FIG. 13 is an isometric view of the transformer 250including various embodiments for attaching auxiliary parking standsthereto. Specifically, the transformer 250 includes parking stand units350, 352 and 354 mounted to an edge 360 of the enclosure 60 to which thecover 58 is secured. The unit 350 includes a mount 364, the unit 352includes a mount 366 and the unity 354 includes a mount 368 that areconfigured to receive the elbow connector 66 or 70 when it is detachedfrom the load-break connector interface 186. Thus, when the cover 58 islifted, the technician can secure one or more of the units 350, 352 and354 to the edge 360 using, for example, securing mechanisms 370 or 372.

FIG. 14 is a simplified schematic diagram of a residential powerdistribution network 400 similar to the network 10. The network 400includes two single-phase, self-powered, magnetically actuated reclosers402 and 404 connected to the same or different feeders (not shown),i.e., at a head end of the network 400, an underground distribution line406 and ten transformers 408, 410, 412, 414, 416, 418, 420, 422, 424 and426 coupled along the line 406 in the manner discussed above. Thetransformer 408 includes switching devices 430 and 432, the transformer410 includes switching devices 434 and 436, the transformer 412 includesswitching devices 438 and 440, the transformer 414 includes switchingdevices 442 and 444, the transformer 416 includes switching devices 446and 448, the transformer 418 includes switching devices 450 and 452, thetransformer 420 includes switching devices 454 and 456, the transformer422 includes switching devices 458 and 460, the transformer 424 includesswitching devices 462 and 464, and the transformer 426 includesswitching devices 466 and 468. The switching device 448 is normally opento provide electrical isolation between the source ends of the network400.

The network 400 will be used below to describe fault isolation and powerrestoration processes when a fault 398 occurs in the line 406 betweenthe transformers 410 and 412 or there is a loss of voltage upstream ofthe network 400, where each of the switching devices 430-466 is similarto the switching device 180 and operate as fault interrupting devices oras sectionalizers that do not provide fault interrupting. For thediscussion below, any reference to detecting overcurrent, detecting lossof voltage, starting timers, sending messages, etc. in the transformersor the switching devices is performed by the shared control unit 256 forthe switching devices in the transformer.

For the fault interrupting embodiment, if the fault 398 occurs in theline 406, the network 400 operates to isolate the fault and restorepower as follows. In order for the fault isolation and power restorationto be performed by the network 400 using the fault interruptingswitching devices, the reclosers 402 and 404 need to have a minimum 1.5power frequency cycle recloser trip. When the fault occurs, the recloser402 will open, the transformers 408 and 410 will log the overcurrentevent and in response to detecting loss of voltage a timer will start inthe transformer 416, which will eventually be used to open the normallyclosed device 448. In response to detecting the overcurrent followed byloss of voltage, one fault interrupter in each of the transformers 408and 410 will open. The recloser 402 will then close in the reclosingoperation after 1.5 cycles, and the transformer 408 will detect voltageon the upstream side of the device 432 and it will close. When thedevice 432 closes, the transformer 410 will detect voltage on theupstream side of the device 434 and it will close. When that happens,the transformer 410 detects overcurrent again due to the fault on theadjacent segment and determines the fault must be on its downstreamside, and thus causes the device 436 to lock open to isolate the fault.When the timer in the transformer 416 expires, the normally openswitching device 448 is closed and in response to the transformer 416detecting overcurrent now from the recloser 404 side of the line 406,the normally open switching device 448 will immediately open and clearthe fault current, but the recloser 404 will not open because its triptime is 1.5 cycles. The transformers 412 and 414 detect the overcurrentfollowed by loss of voltage, and thus the now downstream device 438 inthe transformer 412 and the now upstream device 444 in the transformer414 are opened. The normally open switching device 448 is then closed,and the transformer 414 will detect voltage on the upstream side of thedevice 444 and it will close. When the device 444 closes, thetransformer 412 will detect voltage on one side of the device 438 and itwill close. When that happens, the transformer 412 detects overcurrentagain and determines the fault must be on its downstream side, and thuscauses the device 438 to lock open and isolate the fault on the originalupstream side. In this scenario, it would be required that a workerreset the original configuration of the network 400 when the fault isfixed using the manual handle 188 on the appropriate switching devices430-466.

For the loss of voltage scenario upstream of the network 400, thedevices 430 and 466 are designated “head end” devices. If loss ofvoltage occurs upstream of the recloser 402, the transformers 408, 410,412, 414 and 416 detect the loss of voltage, and a timer is started inthe transformer 408 because it has the head end switching device 430 anda timer is started in the transformer 416 because it has the normallyopen switching device 448, where the timer in the transformer 408 isshorter than the timer in the transformer 416. When the timer in thetransformer 408 expires and loss of voltage is still detected, the headend switching device 430 will open to isolate the source at the recloser402 from the recloser 404, which gives the system time to clear faultsupstream of the recloser 402. The timer in the transformer 416 will thenexpire and the device 448 will close, which will provide power from therecloser 404 to all of the transformers 408-416. In this embodiment, thehead end switching device 430 becomes the normally open switchingdevice. In this scenario, it would be required that a worker reset theoriginal configuration of the network 400 when the source voltagereturns using the manual handle 188 on the appropriate switching devices430-466.

For the sectionalizer embodiment, if the fault occurs in the line 406between the transformers 410 and 412, the network 400 operates toisolate the fault and restore power as follows. In this design, theprotection settings in the reclosers 402 and 404 do not need to bemodified so that, for example, they have a 1.5 minimum trip cycle time,but can be set in any suitable manner. The recloser 402 detects theovercurrent and opens in a fault clearing process, and the switchingdevices 430, 432, 434 and 436 detect the overcurrent, but do not havefault interrupting capability, and detect the loss of voltage when therecloser 402 opens. The switching devices 438, 440, 442, 444 and 446 donot detect the overcurrent, but do detect loss of voltage, and thus thetransformers 412 and 414 start a timer in response thereto, where thetransformer 416 does not start a timer because it has the normally openswitching device 448. The recloser 402 then closes as part of the faultclearing process, detects the overcurrent again and opens again. Inresponse to detecting overcurrent and then loss of voltage a secondtime, the downstream devices 432 and 436 in the transformers 408 and410, respectively, open, and the transformers 408 and 410 send a powerline carrier “clear to close” message on the line 406 to their immediateupstream transformer to close their downstream switching device if theydetected overcurrent, and thus the device 432 closes, but the device 436remains open because the transformer 410 did not receive the clear toclose message. The transformer 408 does send the message upstream, butsince there is not a switching device upstream to receive the messagenothing happens in response thereto. This allows all of the devices430-466 to be the same without the need to provide any in-fieldconfiguration of the devices 430-466 when they are installed. Therecloser 402 then operates a third reclosing sequence test, and sincethe device 436 did not receive the clear to close message and is open,the recloser 402 does not detect overcurrent and remains closed, andpower is restored between the recloser 402 and the transformer 410. Therecloser 402 will then reset all of its protection timings, which do notneed to be coordinated with the devices 430-446.

Subsequently, the timers operating in the transformers 412 and 414 willexpire and since they detected loss of voltage, but did not detectovercurrent and did not receive a clear to close message, they know thatthey are downstream of the fault or a loss of voltage event. In responseto this the upstream devices 438 and 442 in the transformers 412 and414, respectively, will open and the transformers 412 and 414 will senda clear to close message to their immediate downstream transformer thatincludes a unique communications (com) ID generated at runtime. Thedevice 446 is not opened because the transformer 416 knows that it hasthe normally open device 448. The transformer 412 did not receive aclear to close message so the device 438 remains open and the fault isisolated between the transformers 410 and 412. The transformer 414 doesreceive the clear to close message from the transformer 412 so thedevice 442 is closed, and the transformer 416 receives the clear toclose message from the transformer 414, but since it knows that it hasthe normally open device 448 and the device 446 is still closed, itstarts a timer, which allows the system time to make sure the fault isisolated. When the timer in the transformer 416 expires, the device 448is closed, and power is restored to the transformers 412, 414 and 416from the recloser 404. The part of the line 406 between the transformers410 and 412 will then likely be repaired. When workers arrive at thetransformers 410 and 412, they will use the manual lever 188 to lock outthe devices 436 and 438 and prevent them from opening.

If power is lost upstream of the recloser 402, the transformers 408,410, 412, 414 and 416 will go through the process discussed above wherethey do not detect overcurrent, but do detect loss of voltage. When thatoccurs, the transformers 408, 410, 412, 414 and 416 start timers andwhen the timer expires, the upstream devices 430, 434, 438 and 442 inthe transformers 408, 410, 412 and 414, respectively, open and a clearto close message is sent downstream from the transformer 408 to thetransformer 410, from the transformer 410 to the transformer 412, fromthe transformer 412 to the transformer 414 and from the transformer 414to the transformer 416, along with a unique comID generated at run timein the message. Each time a transformer receives a comID it resends thecomID to its downstream transformer so that all of the comIDs areaccumulated in the transformer 416. The messages cause the devices 434,438 and 442 to close, but the device 430 remains open because it didn'treceive a clear to close message and as a result will isolate thenetwork 400. The device 448 does not immediately close because it issubject to the timer in the transformer 416, and when the timer expiresit will close and re-energize all of the transformers 408-416 from therecloser 404.

When power is restored to the recloser 402, it is desirable to returnthe network 400 to its normal state. For the sectionalizer embodiment,when the transformer 408 detects the return of voltage on its upstreamside it will transmit a message along with its comID down the line 406to the transformer 416 to return to the normal state. The comIDs areused to identify the transformers 430-446 as they relay messages fromtransformer to transformer so that messages are not sent to thetransformers 418, 420, 422, 424 and 426 that are not affected by theloss of voltage. The transformer 416 then knows to open the device 448,where power is lost between the transformers 408 and 416, and not tosend the message further downstream. The device 430 is then closed torestore power.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of thedisclosure as defined in the following claims.

What is claimed is:
 1. A method for isolating a fault in a powerdistribution network, the network including a power line, a plurality oftransformers electrically coupled to and positioned along the powerline, a first end switch connected to one end of the power line and asecond end switch connected to an opposite end of the power line, eachtransformer including an upstream switching device and a downstreamswitching device, wherein source power is provided to both ends of thepower line through the first and second end switches and wherein one ofthe switching devices is a normally open switching device, the methodcomprising: detecting overcurrent in the network; opening one or more ofthe one end switch that is delivering power to a section of the networkthat has the fault and at least one of the switching devices in thesection between the one end switch and the fault; detecting loss ofvoltage by the switching devices that are between the fault and thenormally open switching device; closing the switching devices thatdetect voltage on their upstream side and do not detect the overcurrentwhen they close; closing the normally open switching device if itdetects voltage on its upstream side and does not detect the overcurrentwhen it closes; and closing and then opening the switching devices thatdetect voltage on their upstream side and detect the overcurrent.
 2. Themethod according to claim 1 wherein the first and second end switchesare reclosers.
 3. The method according to claim 2 wherein the reclosersare single-phase, self-powered, magnetically actuated reclosers.
 4. Themethod according to claim 1 wherein the upstream switching device andthe downstream switching device in each transformer share a commoncontrol board.
 5. The method according to claim 1 wherein the switchingdevices are fault interrupting devices.
 6. The method according to claim1 wherein closing and then opening the switching devices that detectvoltage on their upstream side and detect the overcurrent occurs in lessthan or equal to 1 current cycle.
 7. The method according to claim 1wherein the power distribution network is an underground powerdistribution network.
 8. A method for isolating a fault in a powerdistribution network, the network including a power line, a plurality oftransformers electrically coupled to and positioned along the powerline, a first recloser connected to one end of the power line and asecond recloser connected to an opposite end of the power line, eachtransformer including an upstream switching device and a downstreamswitching device, wherein source power is provided to both ends of thepower line through the first and second reclosers and wherein one of theswitching devices is a normally open switching device, the methodcomprising: detecting overcurrent in the network from the fault and thenopening the first recloser that is delivering power to a first sectionof the network between the first recloser and the fault; starting atimer in the transformer including the normally open switching device inresponse to detecting loss of voltage when the recloser opens; openingthe downstream switching device in an upstream transformer in the firstsection in response to detecting overcurrent and then loss of voltage;opening the upstream switching device in a downstream transformer in thefirst section in response to detecting overcurrent and then loss ofvoltage; closing the recloser that opened; detecting voltage on theupstream side of the upstream transformer when the recloser closes andopening the downstream switching device in the upstream transformer inresponse thereto; detecting voltage on the upstream side of thedownstream transformer when the downstream switching device closes andclosing the upstream switching device in the downstream transformer inresponse thereto; detecting overcurrent downstream of the transformerand locking the downstream switching device of the downstreamtransformer open in response thereto; closing the normally openswitching device when the timer expires, detecting overcurrent from analternate source as a result of the fault and opening the normally openswitching device; detecting overcurrent and then loss of voltage by thetransformers in a second section of the network between the fault andthe normally open switching device; opening the downstream switchingdevice in an upstream transformer in the second section in response todetecting the overcurrent and then loss of voltage; opening the upstreamswitching device in a downstream transformer in the second section inresponse to detecting the overcurrent and then loss of voltage; closingthe normally open switching device; detecting voltage on the upstreamside of the downstream transformer when the normally closed switchingdevice closes and closing the upstream switching device in thedownstream transformer in response thereto; detecting voltage on theupstream side of the upstream transformer when the upstream switchingdevice is closed and closing the downstream switching device in theupstream transformer in response thereto; and detecting the overcurrentin the upstream transformer and locking the downstream switching deviceof the upstream transformer open in response thereto.
 9. The methodaccording to claim 8 wherein the upstream switching device and thedownstream switching device in each transformer share a common controlboard.
 10. The method according to claim 8 wherein the reclosers aresingle-phase, self-powered, magnetically actuated reclosers.
 11. Themethod according to claim 8 wherein the reclosers have a minimum of a1.5 current cycle reclosing time.
 12. The method according to claim 8wherein closing and then opening the switching devices in response todetecting overcurrent occurs in less than or equal to 1 current cycle.13. The method according to claim 8 further comprising using amechanical handle to open and close the switching devices to reset thenetwork to an original configuration.
 14. The method according to claim8 wherein the power distribution network is an underground powerdistribution network.
 15. A method for restoring power from a loss ofpower event in a power distribution network where the loss of powerevent occurs outside of the network, the network including a power line,a plurality of transformers electrically coupled to and being positionedalong the power line, a first recloser connected to one end of the powerline and a second recloser connected to an opposite end of the powerline, each transformer including an upstream switching device and adownstream switching device, wherein power is provided to both ends ofthe power line through the first and second reclosers, the two switchingdevices closest to the reclosers are designated head end switchingdevices and one of the switching devices is a normally open switchingdevice, the method comprising: starting a first timer in the transformerthat detects loss of voltage from the loss of power event and has a headend switching device; starting a second timer in the transformer thatdetects loss of voltage from the loss of power event and has thenormally open switching device, where the first timer is shorter induration than the second timer; opening the head end switching devicewhen the first timer expires if the transformer still detects loss ofvoltage; and closing the normally open switching device when the secondtimer expires.
 16. The method according to claim 15 wherein the upstreamswitching device and the downstream switching device in each transformershare a common control board.
 17. The method according to claim 15wherein the reclosers are single-phase, self-powered, magneticallyactuated reclosers.
 18. The method according to claim 15 wherein closingand then opening the switching devices in response to detectingovercurrent occurs in less than or equal to 1 current cycle.
 19. Themethod according to claim 15 further comprising using a mechanicalhandle to open and close the switching devices to reset the network toan original configuration.
 20. The method according to claim 15 whereinthe power distribution network is an underground power distributionnetwork.